I. Technical Field
The invention relates to a pressure-driven apparatus, such as pneumatically/hydraulically, for sequentially controlling a multiphase operation, e.g. of a cementing head.
II. Description of the Related Art
From the patent literature, the following is cited as prior art:
EP A2 837.216 discloses a cementing head comprising drop balls being held back by a rotary sleeve actuated by hydraulic or pneumatic pressure. The sleeve is rotated so as to open a port, allowing the ball to fall down the well.
The currently used method of operating a cementing head offshore:
The currently used system is manually operated, i.e. an operator must be lifted 5 to 15 meters above the drilling floor in a riding belt depending on how the cementing head is positioned. When the operator has been lifted up to the cementing head, he turns a handle ½ turn, after which he will be lowered down to the drilling floor. This operation is repeated an additional two times in order to release a cementing plug before and after a cementing job.
The Norwegian Petroleum Directorate has imposed a regulation that this operation is to be carried out by remote control, and that no riding belt is to be used for lifting workers up in the air on offshore installations.